The present invention relates generally to the art of welding-type power supplies. More specifically, it relates to welding-type power supplies having a snubber that recovers energy.
There are many power supplies that produce welding-type power, having a variety of configurations and uses. Welding-type power supply, as used herein, includes power supplies that provide welding-type power. Welding type power, as used herein, refers to welding, plasma or heating power.
TIG welding is one well known welding process, and is often performed using a switched power supply, such as a Miller MaxStar 200(copyright). Switched welding-type power supplies are made with a variety of power topologies and control schemes. Most include a snubber circuit for the switches, that serves to protect switches, such as from voltage spikes.
One disadvantage of snubber circuits is that they tend to increase losses and heating. Accordingly, it is desirable to provide a welding-type power supply that includes a snubber circuit that recovers energy that would otherwise not be utilized.
According to a first aspect of the invention a welding-type power supply includes an inverter power circuit, a bus inductor, a snubber circuit, a snubber capacitor voltage feedback circuit, and a control circuit. The inverter circuit includes a bus, a plurality of switches, and an output. The bus inductor is connected to the inverter and the bus. The snubber circuit is connected to the plurality of switches. Also, the snubber circuit includes a snubber inductor, an isolating diode, a recovery switch connected to the snubber inductor and the snubber capacitor. At least one freewheeling circuit includes the snubber inductor and at least one freewheeling switch. The snubber capacitor voltage feedback circuit is connected to the snubber capacitor and provides a snubber capacitor voltage feedback output to the control circuit. The control circuit includes a comparison circuit that compares the snubber capacitor voltage feedback and a threshold. The output of the comparison controls the recovery switch.
According to a second aspect of the invention a welding-type power supply includes an inverter means for inverting a bus and for providing output power on an output. A snubber means for snubbing the plurality of switches including means for storing and recovering energy, means for opening and closing a current path including the means for storing. The snubber means also includes means for enabling a freewheeling current path that includes the means for storing. Feedback means for providing a signal indicative of a snubber capacitor voltage is connected to the snubber capacitor and a means for controlling the snubber, particularly opening and closing the current path.
According to a third aspect of the invention a welding-type power supply for providing welding-type power includes an inverting means for inverting a bus to provide an output and stabilizing means for stabilizing the bus and the output. A snubber means for snubbing the inverter includes means for recovering energy when a snubber capacitor voltage exceeds a threshold, and means for freewheeling current when the recovery switch is turned off.
A method of providing welding-type power includes inverting a bus to provide an output, stabilizing the bus and the output and snubbing the inverter. Snubbing includes recovering energy when a snubber capacitor voltage exceeds a threshold and freewheeling current when the recovery switch is turned off.
According to one embodiment the recovery switch, snubber capacitor, at least one of the plurality of switches, the load or output, and the snubber inductor form a current path. Also, the freewheeling circuit includes the snubber inductor, the at least one freewheeling switch, the output, and at least one of the plurality of switches.
The inverter is an H-bridge having two current paths in another alternative. The plurality of switches includes at least four switches, and the at least one freewheeling switch includes two freewheeling switches, each associated with one of the H-bridge current paths.
The two freewheeling switches are SCRs and/or the recovery switch is an IGBT in various embodiments.
The welding-type power supply also includes at least one capacitance circuit connected across the bus, and in parallel with the inverter power circuit. A transformer secondary and rectifier is in series with the bus inductor, and the series combination is also in parallel with the capacitance circuit in an alternative.
A diode is disposed between the snubber capacitor and a rail of the bus in yet another alternative.
Other principal features and advantages of the invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description and the appended claims.